The use of a multi-carrier modulation scheme that encodes data onto a radio frequency is known. Orthogonal Frequency Division Multiplexing (OFDM) transmitter, a form of multi-carrier modulation scheme is also known. The use of OFDM to enhance efficient use of the bandwidth as well as to achieve robust communications during multipath interferences is also known.
Prior art OFDM Transmitter chains comprise a variety of components, interfacing to perform the designated functions. The major components in an OFDM Transmitter chain include a Media Access Control (MAC) Interface, a Scrambler, an Encoder, a Puncturer, an Interleaver, an IFFT and a Wave Shaper Block.
In an OFDM transmitter, a Media Access Control (MAC) Interface is configured to convert data to the desired system clock of the OFDM Transmitter. A Scrambler is employed to scramble the serial data coming from MAC. An Encoder enables encoding of the scrambled data bits to generate coded bits. A Puncturer is configured to puncture the encoded bits to meet the data rate constraint.
In an OFDM Transmitter, an Interleaver enables shuffling of data bits to reduce burst error. After shuffling of data bits, a group of data bits are formed. Number of bits in the group depends on the type of modulation. For Binary Phase Shift Keying (BPSK) there is only one bit in the group whereas for 64-Quadrature Amplitude Modulation (64-QAM) 6 bits form a group. This group of data bits map to a particular constellation point depending on modulation type. To normalize the power during transmission, after mapping to a particular constellation point power normalization is done for all the data sub-carriers. This normalization factor depends on the type of modulation.
After mapping to a constellation point, pilots and nulls are inserted at particular position before converting it into time domain OFDM symbol. An IFFT Block converts the frequency domain OFDM symbol to a composite time domain OFDM symbol. Further, to reduce the effect of Inter Symbol Interference (ISI), a Guard Interval is inserted in the IFFT output to form a complete time domain OFDM symbol. This is done by copying a portion of OFDM symbol either at the beginning or at the end. Copying of last few samples is known as Cyclic Prefix Addition.
To reduce the spectral side lobes of the transmitted waveform, transition from one symbol to the other symbol needs to be smooth and at the same time, the transmitted spectral density of the transmitted signal should fall within the defined spectral mask. To achieve this, the Guard Interval inserted OFDM Symbol has to be multiplied with a time domain window. This function is performed in the Wave Shaper block. The Wave-Shaped Transmitted signal is sent to a Radio Transmitter block for up-conversion and amplification before sending it on air.
In known OFDM systems, training symbols are sent at the start of the packet transmission. Therefore, at the start of the packet transmission, the frequency domain-training symbol is converted to time domain by using an IFFT. After Wave shaping it is sent to the radio block for transmission.
Prior art devices are deficient in many respects. These technical deficiencies are with respect to low latency, low gate count, complexity of the components in the system and reduction in the turn around time.
In the prior art systems, in order to support multiple data rate, more than one clock has to be supplied to many blocks in the transmitter. This increases the synchronization logic and increases the complexity of the PLL design.
The current invention addresses the above mentioned issues in respect of low latency in the data transmission, providing multi-rate support, reducing the turnaround time, providing for less complex components in the system and reducing the IFFT latency and the gate count.
It would therefore be desirable to provide systems and methods to address these and other problems